Photodisc/Thinkstock(CHICAGO) -- Some crayons may not be ready for play time, according to a new report.

U.S. Public Interest Research Group, an advocacy group, said in its annual report on the safety of school supplies that Playskool brand crayons purchased at a Chicago Dollar Tree store tested positive for trace amounts of potentially dangerous asbestos chemicals.

The group tested six kinds of crayons from different brands, purchased at stores in several states and online. According to their report, Only the green Playskool crayons tested showed trace amounts of tremolite, a type of asbestos fiber.

Dollar Tree stores acknowledged the report, telling ABC News in a statement, "The safety of our customers and associates is our top priority. Our company utilizes a very stringent and independent testing program to ensure our supplier products meet or exceed all safety and legal standards. We are aware of the report and have since re-verified that each of the listed products successfully passed inspection and testing."

Hasbro, the parent company of Playskool, said it is looking into the reports.

"Product and children’s safety are top priorities for Hasbro," Julie Duffy, senior vice president of global communications for Hasbro, said in a statement to ABC News. "We are conducting a thorough investigation into these claims, including working with Leap Year, the licensee of the product."

According to the report, the crayons U.S. PIRG purchased at the Chicago Dollar Tree were manufactured in China and did not carry an AP seal, meaning an “approved product” certified as non-toxic by The Art and Creative Materials Institute, or ACMI, a manufacturer’s association that promotes safety standards in art materials.

Several other brands of crayons were found to have asbestos fibers in 2000, according to a U.S. Consumer Product Safety Commission study.

CPSC said in its report that it believed the risk that children could be poisoned by coloring with or chewing on tainted crayons was low. But, the commission said, there was no reason crayons should carry the risk at all.

"Although CPSC staff determined that the risk is extremely low, the staff believes that as a precaution, crayons should not contain these fibers. CPSC staff asked the industry to reformulate crayons using substitute ingredients," the report said.

The commission, however, stopped short of regulating or banning asbestos in crayons.

In 2015, four unidentified brands of crayons were found to contain asbestos in tests by the Environmental Working Group.

Other children’s products have recently been found to include asbestos, including makeup kits.

Asbestos refers to a group of minerals that can crystallize into fibers. Because those fibers naturally resist heat and chemicals, they have often been used to make insulation. If these fibers are released into the air and then inhaled by people, they can cause dangerous conditions in the lungs and an aggressive form of cancer called mesothelioma.

Talc, which crayon manufacturers often use as a binder in the wax, can be contaminated with asbestos fibers. Many manufacturers now purify the talc to eliminate asbestos contamination, but there is no specific regulation that requires it.

U.S. PIRG emphasized that its findings this year were mostly positive. Many of the school and art supply products it tested did not contain toxic chemicals.

"The good news is that several years ago, the Consumer Product Safety Commission tested several products and found that many of them had these trace amounts of asbestos and we’re not finding that anymore," Cook-Schultz said. "Now it’s just a matter of getting the law in place to actually make it so that crayons cannot contain asbestos in the U.S."